CVEs-PoC/2021/CVE-2021-21391.md

### [CVE-2021-21391](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-21391)
![](https://img.shields.io/static/v1?label=Product&message=ckeditor5&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=n%2Fa&color=blue)
![](https://img.shields.io/static/v1?label=Vulnerability&message=CWE-400%3A%20Uncontrolled%20Resource%20Consumption&color=brighgreen)

### Description

CKEditor 5 provides a WYSIWYG editing solution. This CVE affects the following npm packages: ckeditor5-engine, ckeditor5-font, ckeditor5-image, ckeditor5-list, ckeditor5-markdown-gfm, ckeditor5-media-embed, ckeditor5-paste-from-office, and ckeditor5-widget. Following an internal audit, a regular expression denial of service (ReDoS) vulnerability has been discovered in multiple CKEditor 5 packages. The vulnerability allowed to abuse particular regular expressions, which could cause a significant performance drop resulting in a browser tab freeze. It affects all users using the CKEditor 5 packages listed above at version <= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.

### POC

#### Reference
- https://www.npmjs.com/package/@ckeditor/ckeditor5-engine
- https://www.npmjs.com/package/@ckeditor/ckeditor5-font
- https://www.npmjs.com/package/@ckeditor/ckeditor5-widget

#### Github
- https://github.com/engn33r/awesome-redos-security